Deoxyribonucleic Acid Synthesis in Oocytes of Mouse Embryos

Abstract

IN order to investigate the synthesis of DNA in mammalian oocytes an attempt was made to label oocytes of mice with a radioactive DNA precursor. If DNA is synthesized during the last premeiotic interphase, as it has been reported for the mouse spermatocyte¹, it should be possible to label oocytes by injecting a radioactive precursor during the last third of pregnancy. Meiotic prophase in the mouse oocyte begins about the 13th day of embryonic life^2–4. Tritium-labelled thymidine was therefore injected into mouse embryos on different days during the latter part of embryonic life to see: (1) whether oocytes can be labelled in this way; (2) what percentage of the oocyte population is labelled after injection on different days of embryonic life; (3) whether labelled oocytes in progressive stages of meiosis can be obtained if autoradiographs are prepared at different intervals after injection of the DNA label.